1. Field of the Invention
The present invention relates in general to a control system for controlling operation of an internal combustion engine, and more particularly to an intake air control system that controls the amount of intake air to a target value by adjusting an OPEN/CLOSE timing of each intake valve of the engine.
2. Description of the Related Art
Hitherto, various intake air control systems have been proposed for appropriately controlling the amount of intake air by controlling the operation timing of the intake and exhaust valves.
One of such intake air control systems is shown in Laid-open Japanese Patent Application 9-256823. In the system of this publication, for accuracy with which the open/close operation of each of the intake and exhaust valves is carried out, an electromagnetic type valve actuating unit is used that includes electromagnetic actuators for actuating the intake and exhaust valves. In the engine equipped with such electromagnetic type valve actuating unit, control of the amount of intake air is made by adjusting the time for which each intake valve is opened, irrespective of whether the intake pipe of the engine is of a type equipped with a throttle valve or a type equipped with no throttle valve. Under operation of the engine, the pressure in the intake pipe is kept substantially equal to the atmospheric pressure, and thus the engine shows a less pumping loss as compared with a conventional engine that controls the intake air by using a throttle valve. However, even such engine has failed to adequately satisfy users due to various reasons.